In general, a system including a tape library device which stores data in a tape cartridge of a magnetic tape or the like and a disk array device which virtually stores the data stored in the tape library device has been used as a virtual tape system.
A general virtual tape system will be described with reference to FIG. 8. FIG. 8 is a diagram illustrating a configuration of a general virtual tape system. As illustrated in FIG. 8, a virtual tape system 900 includes a virtual tape device 910 and a tape library device 920. The virtual tape system 900 is communicably connected to a host 930 which is a higher-level device.
The virtual tape device 910 includes a control server 911 and a disk array 912 and virtualizes the control server 911 and the disk array 912 as a tape library. That is, the virtual tape device 910 causes the host 930 to recognize that the tape library is directly connected to the host 930. The virtual tape device 910 is actually connected to the tape library device 920 at a back-end. The tape library device 920 includes tape drives 921 to which tape cartridges are to be mounted. Data written by the host 930 is temporarily written in the disk array 912, and thereafter, also written in one of the tape cartridges.
Each of the tape drives 921 allows a tape cartridge to be mounted and writes data to and reads data from the mounted tape cartridge using a magnetic head. When data is written and read a certain number of times, the magnetic head gets dirty. In this case, an error occurs frequently when data is written or read, and accordingly, retry is frequently performed. Therefore, the magnetic head is to be cleaned.
FIG. 9 is a diagram illustrating general cleaning control. In the example of FIG. 9, the tape library device 920 has a cleaning control function. Specifically, the tape library device 920 executes the cleaning control and when receiving a cleaning request from one of the tape drives 921, the tape library device 920 cleans a magnetic head of the tape drive 921 which has issued the cleaning request.
Some tape library devices do not have the cleaning control function. Such a tape library device does not automatically perform cleaning of tape drives. Therefore, a user temporarily interrupts operation, manually performs cleaning of the tape drives, and thereafter, the operation is started again.
In a magnetic tape device connected to a higher-level device, a technique is employed in which the magnetic tape device adds up lengths corresponding to movements of a tape. When a value obtained by the adding up reaches a preset value, the magnetic tape device requests the higher-level device to perform cleaning, until the cleaning is executed, every time an instruction for unloading a magnetic tape is issued from the higher-level device.
Japanese Laid-open Patent Publication No. 01-256013, Japanese Laid-open Patent Publication No. 07-302131, and Japanese Laid-open Patent Publication No. 2003-331408 disclose related techniques.
A general virtual tape system has a problem in that a host is not capable of managing cleaning of tape drives. In a case of a tape library device having a cleaning control function, since the tape library device performs cleaning control, a host which is not directly connected to the tape library device is not capable of managing cleaning of tape drives. Also in a case of a tape library device which does not have a cleaning control function, since the tape library device is not capable of performing cleaning control, a host which is not directly connected to the tape library device is also not capable of managing cleaning of tape drives.
In a case of a magnetic tape device which is connected to a higher-level device, if a device corresponding to a virtual tape device is disposed between the higher-level device and the magnetic tape device, the magnetic tape device is not capable of transmitting a cleaning request to the higher-level device, and accordingly, the higher-level device is not capable of transmitting a cleaning request to tape drives.
As illustrated in FIG. 9, in the general cleaning control, tape control software describing a function of controlling cleaning of tape drives is installed in a host in some cases. In this case, the host is capable of controlling the tape library device by executing the tape control software installed in the host when the tape library device is directly connected to the host, and otherwise, the host is not capable of controlling the tape library device. Accordingly, the host is not capable of controlling cleaning of the tape drives included in the tape library device.
Note that the problems described above occur not only in magnetic heads of tape drives but also in reading heads and writing heads for general tapes such as paper tapes.